Nintendo has today announced that the Wii smashed all retail records in December 2009, with the console selling over 3.8 million units, a new all-time single-month US sales record. Of all the Wiis ever sold in the US since its November 2006 launch, nearly one-fifth were sold during November and December 2009. Wow!

“Wii, Nintendo DS Lite and Nintendo DSi combined to sell more than 7 million units in the month of December alone,” said Cammie Dunaway, Nintendo of America’s executive vice president of Sales & Marketing. “Clearly there is overwhelming consumer demand for fun games, motion controls and value. This remarkable hardware sales surge presents a tremendous software opportunity for Nintendo and its third-party partners as we head into 2010.”

And it’s not just the hardware that’s selling well. In December alone, there were six Nintendo games in the top 10 best-sellers of the month, including New Super Mario Bros. Wii at No. 1 with more than 2.8 million sold, Wii Sports Resort at No. 2 with more than 1.7 million sold, and Wii Fit Plus with Balance Board at No. 3 with more than 1.7 million sold.